Multiple-glazed, insulating window units usually consist of two (or more) panes of glass maintained in spaced, parallel relation to each other by a spacing and sealing assembly which is structurally bonded to the marginal edge periphery of opposed, inner or facing surfaces of the glass panes to define a hermetically sealed, insulating airspace between the panes. The spacing and sealing assembly hermetically seals the airspace from the environment. The spacing and sealing assembly generally contains a desiccant material or dehydrator agent for adsorbing moisture or water vapor which may be present in the airspace when the units are assembled or which may later diffuse through the sealant of the spacing and sealing assembly to ensure dryness of the airspace, to prolong the useful life of the unit, and to enhance the performance quality thereof. Representative examples of multiple-glazed, insulating window units are taught in U.S. Pat. Nos. 2,306,327; 2,838,810; 3,280,523; 3,733,237; 3,791,910; 4,226,063 and 4,348,435, which teachings are herein incorporated by reference.
When the sealed, insulating window units of the above-discussed type are subjected to pressure differential between the airspace and the exterior atmosphere, the pressure differential will result in deflection of the glass panes. Pressure differential may be caused in a multiplicity of ways, e.g. by the atmospheric pressure whereat the window unit is installed being different than the pressure conditions which existed when the unit was sealed and/or by large temperature differences between the airspace and the exterior atmosphere, e.g. during large atmospheric temperature changes. When the pressure between the panes is less than the exterior pressure, the panes are forced closer together. Conversely, when the pressure in the space exceeds the exterior pressure, the panes are forced apart. Appreciable deflection of the panes can cause optical distortion of the window unit and can also present an undesirable cosmetic effect. Further, appreciable deflection places stress on the spacing and sealing assembly which may weaken the adhesive bond between the glass surfaces and the spacing and sealing assembly and ultimately cause a separation therebetween. This phenomenon may result in leakage and infiltration of relatively moist exterior air into the insulating airspace, ultimately causing saturation and exhaustion of the desiccant contained by the spacer element. When the desiccant is exhausted, it is no longer capable of adsorbing the moisture-vapor present in the airspace, and condensation of the moisture-vapor begins to occur on the glass surfaces contacting the airspace hereinafter referred to as interior glass surfaces. More specifically, the moisture-vapor forms a molecular film of water on the interior glass surfaces. The molecular film absorbs or leaches molecules or ions from the glass surfaces. This leaching phenomenon is evident/is manifested as scum or stain on the interior glass surfaces, which imparts an undesirable white hazy or foggy appearance to the window unit. As can now be appreciated, the sealed insulating window units of the instant discussion are preferably used where pressure differentials are insufficient to cause a separation between the glass pane and spacing and sealing assembly.
Multiple-glazed window units of the type taught in U.S. Pat. Nos. 3,771,276; 3,838,809 and 4,455,796 minimize the above-discussed deflection and desiccant saturation problems by providing facilities to equalize the air pressure in the airspace to the ambient air pressure while keeping the airspace relatively free of moisture. In general, U.S. Pat. No. 3,771,276, assigned to the assignee of the present invention, teaches a multiple-glazed unit having a breather device comprised of a capillary tube connected to a column of desiccant, so that a free end of the capillary tube is disposed in open communication with the air surrounding the unit (i.e. the exterior atmosphere) while the desiccant column, to which the capillary tube is fluidly connected at its opposite end, is in communication with the enclosed, insulating airspace of the unit. In operation, the breather unit works in the following manner. When the exterior atmospheric pressure exceeds the air pressure of the insulating airspace, e.g. due to a nighttime temperature drop, air flows from the exterior atmosphere, through the capillary tube and the desiccant column, and thenceforth, into the insulating airspace. During this inflow of the exterior atmospheric air, moisture contained in the entering air is adsorbed by the desiccant. Further, the airspace pressure and the exterior atmospheric pressure are equalized, thereby preventing deflection of the opposed glass panes. Conversely, when the air pressure of the insulating airspace exceeds the pressure of the exterior atmospheric air, e.g. due to warmed air expansion during daytime hours, then air flows from the insulating airspace, through the desiccant column and the capillary tube, and thenceforth, into the exterior atmosphere. The warm, outflowing air desorbs the previously adsorbed moisture from the desiccant, thereby regenerating the desiccant and extending its useful life. Further, the airspace pressure and the exterior atmospheric pressure are equalized, thereby eliminating deflection of the glass panes. U.S. Pat. No. 4,455,796 issued to Schoofs teaches an insulating glass unit similar to that taught in U.S. Pat. No. 3,771,276 discussed above. In general, the unit of Schoofs has a breather device for minimizing deflection of the glass panes and maximizing the useful life of the desiccant. U.S. Pat. No. 2,838,809, assigned to the assignee of the present invention, in general, teaches a unit having a plurality of glass sheets separated at their marginal edges by a hollow spacer element containing a desiccant material, an elongated strip of mastic in sealing contact with the edges of the glass sheets and the spacer element, and a pressure sensitive tape covering the strip of mastic. The unit is provided with an aperture or aligned opening through the tape, mastic and outer wall of the spacer element to connect the atmosphere with the desiccant, and at least one other opening through the inner wall of the spacer element communicating with the insulating airspace of the unit. The aligned openings or apertures permit the unit to "breathe" through the desiccant material in response to changes in atmospheric conditions.
All of the above-discussed presently available insulating window units are acceptable in one or more applications; however, as can now be appreciated, not every unit is ideally suitable for every use. It would be advantageous therefore to provide a multiple-glazed window unit having features which make the unit less expensive to manufacture than the presently available units while eliminating the limitations of the presently available units.